A small, unobtrusive system for accurate measurement of blood alcohol concentration would have wide application in monitoring alcohol consumption and metabolism for clinical, research, and criminal justice purposes. Desirable features include: an alcohol assay method that is sensitive, precise, and accurate; a sampling method that is reliable and provides results directly linked to the alcohol concentration in the blood; on-chip power and data storage; and a clear indication of tampering. This need can be met with a unique new device based on the synergy of two technologies-- the silicon microsampling and assay chip pioneered in the applicant's laboratory for painless blood testing, and an integrated electrochemical alcohol biosensor. The chip includes a microprobe finer than a human hair that can penetrate skin reliably and painlessly. The disposable silicon microchip can be cost-effectively produced by MEMS (microelectromechanical systems) technology. The packaged device does not require expert medical intervention to affix or remove, and can be worn anywhere on the skin. It consists of an adhesive strip resembling a Band-Aid with a two-millimeter long silicon microprobe with electrochemical sensor that protrudes into the skin, plus signal processing circuitry and data storage in an integrated button-like housing. The silicon microchips and electronic instrumentation to perform the sampling step and electrochemical readout will be adapted from devices currently being made by the applicant for diabetic glucose self-testing.